Ions and Electrons
Like electrons, ions themselves can produce ionization when their velocity has become sufficiently large. If one's finger is placed near to a rod of glass which has been rubbed, a slight crackling noise can be heard, and if the experiment is performed in a darkened room a very weak glow can be seen. The phenomenon can be made clearer by placing two spheres at a few millimetres distance from one another and charging them until a spark passes between them. If a Leyden jar is discharged, the noise which accompanies the passage of the spark becomes much more intense. This phenomenon can be much more easily observed with lower potential differences by placing two pieces of metal, which form the electrodes, opposite to one another in a vessel from which the air can be removed. At lower pressures the band breaks up into striations which are separated by dark spaces.